1. Field of the Invention
The present invention relates to a sheet processing apparatus that has a function of aligning sheets stacked on a stack tray, a control method for the sheet processing apparatus, and a storage medium.
2. Description of the Related Art
For sheet processing apparatuses that stack a large number of sheets, there has been demand for the ability to discharge and align the sheets with a high degree of accuracy. Japanese Patent Laid-Open No. 2006-206331 suggests a sheet alignment process in which alignment members are provided on a stack tray, and sheets are piled up in such a manner that the positions of edge surfaces of the sheets parallel to a sheet discharge direction are lined up by the alignment members coming into and out of contact with the edge surfaces of the sheets.
The aforementioned conventional technique has the following problem. For example, if a user removes a part of sheets stacked on the stack tray, there is a possibility that sheets stacked on the stack tray may be misaligned. If an alignment process is applied to the sheets on the stack tray in this state, the sheet quality could possibly be reduced due to bending of the sheets stacked in a misaligned manner, and due to sliding of the bottom surfaces of the alignment members against the sheets stacked in a misaligned manner.